When two user equipment terminals (e.g., mobile communication devices) of a cellular network or other telecommunication system communicate with each other, their data path typically goes through the operator network. The data path through the network may include base stations and/or gateways. If the devices are in close proximity with each other, their data path may be routed locally through a node such as a local base station. In general, communications between a network node such as a base station and a wireless terminal is known as “WAN” or “Cellular communication”.
It is also possible for two user equipment terminals in close proximity to each other to establish a direct link without the need to go through a base station. Telecommunications systems may use or enable device-to-device (“D2D”) communication, in which two or more user equipment terminals directly communicate with one another. In D2D communication, voice and data traffic (referred to herein as “communication signals”) from one user equipment terminal to one or more other user equipment terminals may not be communicated through a base station or other network control device of a telecommunication system. Device-to-device (D2D) communication has more recently also become known as “sidelink direct communication”
D2D communication, e.g., sidelink direct communication, can be used in networks implemented according to any suitable telecommunications standard. A non-limiting example of such as standard is the 3rd Generation Partnership Project (“3GPP”) Long Term Evolution (“LTE”). The 3GPP standard is a collaboration agreement that aims to define globally applicable technical specifications and technical reports for third and fourth generation wireless communication systems. The 3GPP may define specifications for next generation mobile networks, systems, and devices. The 3GPP LTE is the name given to a project to improve the Universal Mobile Telecommunications System (“UMTS”) mobile phone or device standard to cope with future requirements. In one aspect, UMTS has been modified to provide support and specification for the Evolved Universal Terrestrial Radio Access (“E-UTRA”) and Evolved Universal Terrestrial Radio Access Network (“E-UTRAN”). E-UTRAN is another non-limiting example of a telecommunications standard with which D2D communication may be used.
Device to device (D2D) communications provide proximity-based applications and services, representing an emerging social-technological trend. The introduction of a Proximity Services (ProSe) capability in LTE allows the 3GPP industry to serve this developing market, and, at the same time, serve the needs of several Public Safety communities that are jointly committed to LTE. The current assumptions related to D2D communication is that a wireless terminal within network coverage uses resources for D2D discovery and communication assigned by the controlling node. If the wireless terminal is out of network coverage, it may use pre-assigned resources for communications.
D2D services include ProSe Direct Communication (e.g., D2D communication, sidelink direct communication) and ProSe Direct Discovery (e.g., D2D discovery, sidelink direct discovery). ProSe Direct Communication is thus a mode of communication whereby two wireless terminals may communicate with each other directly over the PC5 interface (See, e.g., 3GPP TS 23.303 VER 12.0.0, which is incorporated herein by reference in its entirety). ProSe Direct Communication is supported when the wireless terminal is served by E-UTRAN and when the wireless terminal is outside of E-UTRA coverage. A transmitter of the wireless terminal transmits Scheduling Assignments (SA) to indicate the resources it is going to use for data transmission to the receiver wireless terminal involved in the D2D communication.
FIG. 11 shows the protocol stack for the user plane, where PDCP, RLC and MAC sublayers (terminate at the other UE) performs various the functions, such as (for example) header compression and HARQ retransmissions.
A ProSe-enabled wireless terminal may operate in two modes for resource allocation. In Mode 1 the network node (e.g., eNodeB) allocates the resources to be used for the device-to-device (D2D) communication. In D2D Mode 1, the wireless terminal needs to be RRC_CONNECTED in order to transmit data. Moreover, the wireless terminal requests transmission resources from the eNB. The eNB schedules transmission resources for transmission of scheduling assignment(s) and data. Further, the wireless terminal sends a scheduling request (D-SR or Random Access) to the eNB followed by a buffer status report (BSR). Based on the BSR the eNB can determine that the wireless terminal has data for a ProSe Direct Communication transmission and estimate the resources needed for transmission.
In D2D Mode 2 the wireless terminal autonomously selects the radio resources to be used for D2D communication. In particular, a wireless terminal on its own selects resources from resource pools to transmit scheduling assignment and data.
A wireless terminal is considered in-coverage if it has a serving cell (i.e. the UE is RRC_CONNECTED or is camping on a cell in RRC_IDLE). If the wireless terminal is in coverage it may use mode 1 if the eNB configures the wireless terminal to use Mode 1. A wireless terminal is said to be out of coverage it can only use Mode 2. However, if the wireless terminal is in coverage it may use Mode 2 if the eNB configures the wireless terminal to use Mode 2. If the wireless terminal is in coverage it shall use only the mode indicated by eNB configuration unless an “exceptional case” occurs. When an exceptional case occurs the wireless terminal may be allowed to use Mode 2 temporarily even though it was configured to use mode 1.
As understood from the foregoing, the resource pool used for reception of a Scheduling Assignment when the wireless terminal is in coverage is configured by the eNB via RRC, in dedicated or broadcast signaling. However, the resource pool used for transmission of Scheduling Assignment when the wireless terminal is in coverage may be configured by the eNB via RRC if Mode 2 resource allocation is used. The SA resource pool used for transmission when the wireless terminal is in coverage is not known to the wireless terminal if Mode 1 resource allocation is used. The eNB schedules the specific resource(s) to use for Scheduling Assignment transmission if Mode 1 resource allocation is used. The specific resource assigned by the eNB is within the resource pool for reception of Scheduling Assignment that is provided to the wireless terminal.
The radio resource pool used for reception of Scheduling Assignments when the wireless terminal is out of coverage is pre-configured. Similarly, the resource pool used for transmission of Scheduling Assignments when the wireless terminal is out of coverage is pre-configured.
In order to perform communication even when some wireless terminals are in-coverage and some wireless terminals are out of coverage, all wireless terminals (i.e. both in and out of coverage) should monitor the resource pool for Scheduling Assignment which is the union of the resource pools used for transmission of Scheduling Assignment in all (or some of the when in-coverage) cells and transmission of Scheduling Assignment out of coverage.
To date several popular distributed resource allocation algorithms have been suggested for resource allocation in device-to-device (D2D) Mode 2 communications. Among the proposed distributed resource allocation algorithms are random resource selection, Randomized Resource Patterns for Transmission (RPT) selection (RRPT), and Carrier Sense Multiple Access With Scheduling Assignment (SA) Blind Decoding (CSMA/SA). Utilization of one universally-applied resource access/allocation method may be problematic and inefficient.
What is needed, therefore, are methods, apparatus, and/or techniques for allocating radio resources for sidelink direct communications.